1. Field of the Invention
The present invention relates to a spectroscope equipped with a spectroscopic element for dispersing input light from an input portion and a microspectroscope equipped therewith.
2. Related Background Art
A diffraction grating has been widely used as a spectroscopic element for a spectroscope. The diffraction grating has polarization dependency, so that diffraction efficiency thereof is generally considered to be higher in S-polarized light that the direction of electric field oscillation thereof is perpendicular to the direction of grooves of the diffraction grating than in P-polarized light that the direction of electric field oscillation thereof is parallel to the direction of grooves of the diffraction grating. In particular the long wavelength range where the wavelength of the incident light is comparable or longer than the period (a pitch of the grooves) of the diffraction grating, the tendency becomes conspicuous. In other words, the shorter the period of the diffraction grating becomes, the more conspicuous the tendency appears, so that when a diffraction grating with high resolution is used, it should be noted.
Accordingly, in order to solve the difference in diffraction efficiency according to direction of polarization, a technique is disclosed in U.S. Pat. No. 6,498,872 B2.
The technique is to arrange the direction of polarization of the incident light into the diffraction grating. In particular, the light coming out from an incident port is divided into P-polarized light and S-polarized light by a polarizing beam splitter, the P-polarized light is converted into S-polarized light by half wave plate, and the S-polarized light beam and the S-polarized light beam converted from the P-polarized light are led to a diffraction grating parallel with each other.
In the technique disclosed in U.S. Pat. No. 6,498,872 B2, since the directions of polarization of the incident light into the diffraction grating are arranged, the problem according to polarization dependency of the diffraction grating is solved. However, since the S-polarized light and the S-polarized light converted from the P-polarized light are incident to the diffraction grating on respective areas different with each other, the diffraction grating becomes large resulting in a problem that the instrument becomes large and costly.